1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device capable of preventing misattachment of a polarizing plate, and a manufacturing method thereof.
2. Discussion of the Related Art
Since liquid crystal display devices (LCDs) have low power consumption and high portability through integrated technology, they are considered as a next generation of high-tech display device. The LCD is an image display device that includes liquid crystal injected between an array substrate and a color filter substrate. The array substrate includes thin film transistors (TFTs). The LCD displays an image by using a light refractive index difference according to liquid crystal anisotropy.
An active matrix liquid crystal display (AMLCD) is mainly used in a flat display field. One thin film transistor is used as a switching element to change light transmittance by controlling a voltage applied to the liquid crystal of one pixel. Amorphous silicon:H (hereinafter, referred to as amorphous silicon) is mainly used for a TFT because it can be easily manufactured in a large size.
In manufacturing the LCD, red (R), green (G) and blue (B) color filters are sequentially formed on a top substrate using photolithography, a thin film transistor as a switching element and pixel electrodes are sequentially formed on a bottom substrate using photolithography, and the top substrate and the bottom substrate are attached to each other. Then, an LCD is formed by injecting liquid crystals.
A spacer is dispersed between the substrates to maintain a cell gap between the top substrate and the bottom substrate, and a seal printing process is performed to attach the top substrate and the bottom substrate and seal the liquid crystals.
The subsequent processes after the attachment process will now be described. FIG. 1 is a schematic view illustrating a related art manufacturing process of an LCD.
Referring to FIG. 1, a seal is printed on a TFT with a thin film transistor, and a spacer is dispersed on a color filter substrate (C/F). Then, the two substrates are combined together. The attachment of the substrates is performed with heat, pressure, and ultraviolet irradiation after the TFT substrate is aligned with the color filter substrate. Then, the combined substrate is cut into cells.
When the cell process is completed, liquid crystal is injected into each liquid crystal cell. Then, the injection hole is sealed after the injection process using an ultraviolet hardening resin. A polarizing plate is attached to the liquid crystal cell after liquid crystal is injected into the liquid crystal cell. Attachment of the polarizing plate is performed to press the polarizing plate to the liquid crystal cell using a roller after the polarizing plate is aligned with a liquid crystal surface.
The polarizing plate plays a role in selectively transmitting light polarized in a predetermined direction from light passing through the liquid crystal. The image quality of the LCD display deteriorates if the polarizing plate is not precisely attached to the liquid crystal cell.
After a top polarizing plate and a bottom polarizing plate are attached to the liquid crystal cell, a defect test is applied. The defect test includes determining the lighting status of the liquid crystal cell and whether or not stains are present. The defect test is performed by applying a test signal to a pad region of the liquid crystal cell. Then, a finished LCD is completed by attaching a circuit substrate to the liquid crystal cell.
However, referring to FIG. 2, misattachment of the polarizing plate 15 frequently occurs in the related art process of attaching a polarizing plate. This occurs as there is often misalignment between the liquid crystal cell 10 and the polarizing plate 15 before the polarizing plate 15 is attached to the liquid crystal cell 10.
FIG. 2 is a plan view illustrating a related art misattachment of a polarizing plate during the process of attaching a polarizing plate. As shown, the polarizing plate 15 is attached to an active area 11 of an image display region, but is tilted during the attachment process.
The misattachment of the polarizing plate occurs because an alignment reference of the polarizing plate 15 and the liquid crystal cell 10 is ambiguous, and the attachment process is performed using a roller right after the polarizing plate 15 is mechanically aligned with the liquid crystal 10. In particular, it is difficult to detect twisting of the polarizing plate when the polarizing plate is attached to the active area 11 of the liquid crystal cell 10.